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DNA contamination: safeguarding forensic samples

Professor Greg Hampikian has developed a DNA barcode system that permanently marks DNA samples, preventing them from being muddled with others.

Professor Hampikian, who is chair in Biological Sciences and Criminal Justice at Boise State University, says DNAcontamination is a fact of life in all laboratories. He has worked on many Innocence Project cases overturning wrongful convictions around the world, including the high-profile Amanda Knox murder conviction case in Italy.

DNA evidence is invisible and remarkably easy to transfer, making it possible for a sample to be spilled or even planted on a piece of evidence.

Contamination compounded by copying techniques

In a press release from Boise State University, Professor Hampikian said the problem of contamination is compounded by techniques that make billons of copies of DNA and new instruments that detect even just a few molecules. “Unfortunately, samples taken from victims and other innocent people are still processed in the same place as samples from weapons, bodies and other evidence.”

Professor Hampikian has been working on his barcoding system for more than a decade, and he and his team recently demonstrated its effectiveness for the first time. The results of the work are in press in the Journal of Forensic and Legal Medicine and were published online on 16 April 2013.

Nullomer tags clearly detected

Professor Hampikian and his team used nullomers, the smallest DNA sequences that are absent from nature, to create the DNA barcode. This barcode could be integrated with DNA samples at the time of collection, and the detection of this barcode would indicate that the source of analysed DNA was from a reference sample provided by an individual and not from an evidence sample.

“We demonstrate that the nullomers can be added directly to collection devices (FTA paper) to allow tagging during the process of sample collection. We show that such nullomer oligonucleotides can be added to existing forensic typing and quantification kits, without affecting genotyping or quantification results. Finally, we show that, even when diluted a million-fold and spilled on a knife, the nullomer tags can be clearly detected. These tags support the National Research Council of the National Academy recommendation that ‘Quality control procedures should be designed to identify mistakes, fraud and bias’ in forensic science,” the researchers wrote in their published research.

Nullomers identified

Several years ago, Professor Hampikian and colleague Tim Andersen identified the tiny DNA and protein sequences that were absent in nature, and Professor Hampikian termed these sequences ‘nullomers’. At the time, the researchers proposed that these sequences could have properties that were incompatible with life and might serve as drugs to kill pathogens and even cancer. Other research has been on-going in this area.